This invention relates generally to a material handling apparatus and more particularly to a material handling apparatus having a rotatable upper structure which is releasably connected to a base and to a bearing mounted for high load bearings.
Cranes and other material handling vehicles commonly have rotatable booms and operator's cabs, generally referred to as the bearing is provided for supporting the upper structure on the base while providing for rotation about a vertical axis and transmitting axial, radial and moment forces from the upper structure to the base.
It is highly desirable to be able to quickly connect and disconnect the upper structure with respect to the base. By disconnecting the upper structure from the base, the bearing may be readily repaired, maintained or replaced. The need to separate the upper structure from the base frequently occurs when the crane must be shipped over highways to a new job site. Depending on the size of the crane or other machine with a rotatable upper structure, highway axle load limits might otherwise be exceeded. In addition, difficulty may be encountered clearing low bridges necessitating taking an undesirable route to the job site. By disconnecting the upper structure from the base, which in some cases may be a mobile carrier, the upper structure may be shipped on a flat bed truck while the stripped mobile carrier moves under its own power.
Several arrangements for releasably mounting the upper structure including the bearing to the base are known. Most commonly the upper structure is connected to the bed by use of bolts which are torqued to provide high clamping forces on the bearing raceways. A connection of this type is shown in Mork et al, U.S. Pat. No. 3,125,226. These bolts must be pre-loaded by torquing to a uniformly high value. High and uniform tensile forces in a large number of camping bolts necessitate considerable labor and a substantial amount of time to connect or disconnect the upper structure to and from the base. Yet another problem with this design is that bolts in tension are susceptible to fatigue failure, particularly as bolt preload is lost through embedment and lack of maintenance.
The upper structure has also been connected to the base by using bolts (see Manly U.S. Pat. No. 2,313,084) or rollers whose axis extends radially of the swing axis of the upper structure, problems arise with these structures. In the case of bolts as in the Manly patent, a large number of bolts are required as compared to the use of tensioned bolts extending parallel to the axis as shown in the Mork patent. The shear strength of steel bolts used in a single shear arrangement is less than its tensile strength based on commonly used yield stress criteria. In addition, the bolts as used in the Manly patent have a tendency to bend and cock, making disconnection of any bent or cocked bolts or pins difficult. The bending stresses introduced by this action further reduce the usable load capacity of the connection.
Yet another prior art design is shown in Short, U.S. Pat. No. 3,726,418 which uses a number of tangs and which are extensions of the inner race of the bearing. The tangs are received in corresponding openings in the carrier. A tapered wedge block assembly is driven to a slot in each of the tangs to connect the upper structure and the bed or carrier. Such a design is not readily and easily disconnectable and is quite expensive to build. The wedge block assembly is accessible only from the underside of the carrier thus increasing the difficulty of connecting and disconnecting the upper structure with respect to the carrier.
To obtain an easy disconnect of the upper structure and bearing, various designs have been proposed utilizing circumferential clamps between flanges on the bearing and bed including hydraulically operated clamps. Such arrangements have problems in securing the parts tightly and providing room for the clamp operation and are generally expensive and complicated.
It may be understood that a quick connect device for interconnecting an upper structure to a carrier or base allowing for ease of alignment both in transverse placement and angular orientation is desirable. It is also desirable that a quick connect device be low in cost and the fasteners be standard in size and minimum in number. It is also desirable that the fasteners are not required to have a high pre-load torque which requires uniform and sequential loading of the bolts as well as making it difficult to disconnect. Also, eliminating the need for bolt preload decreases the amount of labor and time involved in the connection or disconnection process. It is also desirable that the quick connect design provides for long fatigue life of the parts effecting the quick disconnect device.